Noise issue in animation
The denoiser is only suited to certain situations - in some cases it can actually cause unwanted artifacts and noise; it is generally best suited to well lit, less noisy renders to tidy up a small amount of noise or bright spots caused by caustics. In your case your raw render simply contains too much noise for the denoiser to produce consistent results between different frames of the animation.

To demonstrate, I created a noisy test scene with a banded material similar to your 'skin' and rendered three times : without the denoiser, with the denoiser, with more samples.

Here's the 'raw' noisy render (32 samples) :



The denoiser can help considerably for individual frames but when animated the denoising slips between frames causing artifacts (click the image to see it full size) :



Note how the darker benoised areas seem to wash around and move in subsequent frames of the animation.

An alternative to the denoiser is to simply render with more samples (256 samples) :



This takes more time to render but produces much more consistent images between consecutive frames.

It's difficult to see from the above images so here is a comparison on a zoomed section of the denoised and more sample animations :

Denoised : 

More samples : 

Note the fuzziness caused by the denoiser throughout. The 'more samples' result is generally much more stable (except where the banding is inteferring with the pixel width - causing the rippling at the start/end).

So, in summary, in your particular case, the details of the 'skin' and the low light and shadows are a case where the denoiser causes considerable artifacts. It would be acceptable for still frames but not for animation. Your only solution is to disabled the denoiser and render with more samples (but this will considerably increase render times).